1. Field of the Invention
The present invention relates to a semiconductor device and a semiconductor device manufacturing method and, more particularly, to a thermal annealing technology.
2. Description of the Related Art
High integration of LSIs has been achieved by reducing sizes of elements constructing LSIs. With decreasing dimensions of elements, the formation of a shallow p-n junction, i.e., the formation of a shallow impurity diffusion region is becoming important.
To form this shallow impurity diffusion region, ion implantation at low acceleration energy and optimization of subsequent annealing are important. Boron (B) is used as a p-type impurity, and phosphorus (P) and arsenic (As) is used as an n-type impurity. However, these impurities have larger diffusion coefficients in silicon (Si). Therefore, these impurities diffuse inward and outward when RTA (Rapid Thermal Anneal) using a halogen lamp is performed. This gradually makes it difficult to obtain a shallow impurity diffusion layer. If the annealing temperature is lowered to suppress impurity diffusion, the activation ratio of the impurity largely decreases. By RTA using a halogen lamp, therefore, it is difficult to form an impurity diffusion layer having a shallow (about 20 nm or less) junction and low resistance.
To solve the above problem, a flash lamp annealing method using a xenon (Xe) flash lamp is being studied as a method of momentarily supplying energy required for activation. A Xe flash lamp is obtained by sealing Xe gas in a tube such as a quartz tube. This Xe flash lamp can emit white light within the range of, e.g., a few 100 μsec to a few msec by discharging electric charge stored in a capacitor within a short time period. Accordingly, an impurity can be activated without changing the distribution of impurity ions implanted into a semiconductor layer.
Unfortunately, the light of the flash lamp is reflected by the surface of a semiconductor substrate to worsen the heating efficiency. This makes sufficient impurity activation difficult. If the irradiation energy of the flash lamp is increased to raise the activation ratio, the thermal stress increases, and this destroys the semiconductor substrate. That is, the conventional flash lamp annealing method can form an impurity diffusion region having a shallow junction but cannot unlimitedly lower the resistance of the diffusion layer.
Another conventional technique known to those skilled in the art is to form a light-absorbing film to efficiently absorb lamp light during annealing. Jpn. Pat. Appln. KOKAI Publication No. 10-26772 discloses a technique which forms a light-absorbing film on the surface of a gate insulating film in the fabrication of a TFT (Thin Film Transistor). Since, however, the light-absorbing film formed on the surface of a gate insulating film is used, efficient heating is difficult to perform. Jpn. Pat. Appln. KOKAI Publication No. 2000-138177 discloses a technique which forms a light-absorbing film on the surface of an interlayer insulating film in the fabrication of a semiconductor device. However, the use of the light-absorbing film formed on the surface of an interlayer insulating film also makes efficient heating difficult.
As described above, as the integration degree of LSIs increases, it is becoming important to control the impurity profile with high accuracy, e.g., to form a shallow, low-resistance impurity diffusion layer. However, accurately controlling the impurity profile is conventionally difficult.